This invention relates to electrical connections between data/servo flex circuits and magnetic heads in a disc drive. More particularly, this invention relates to a novel technique for effecting electrical connections between a thin film head on one end of a Whitney Suspension Mechanism (WSM) and a flex circuit which is at the other end of the WSM. The novel electrical connection provides an industry standard assembly which may be used by different disc drive manufacturers and involves the use of a controlled impedance flexible circuit and a matched impedance solderless connection.
The Whitney Suspension Mechanism (WSM) is also known as the Whitney Flexure. It is a small spring-steel suspension arm approximately 1 inch long. It is simpler and more stable than Winchester flexures which have preceded the WSM. The WSM is a delicate structure with special aerodynamic and mechanical properties which ensure that the thin film head is reliably positioned at a precise distance and orientation with respect to the surface of a rigid, rotating disc in a magnetic memory.
Typically, the WSM is attached to a rigid arm which is controlled by an electro-mechanical servo-mechanism. The arm is normally constructed of aluminum. During operation, the motion of the arm positions the magnetic head over a given track on the disc, while the WSM positions the magnetic head at a given distance and orientation relative to the disc surface.
Usually, a flexible printed circuit is bonded to this rigid arm. The flexible circuit provides a set of conductive leads which define electrical paths for the transmission of electrical signals between the thin film head and the electronic components in the disc system control. Typically, an integrated circuit and certain passive components, are soldered to the flexible circuit near the end of the arm to (1) control the operation of the thin film head; and (2) condition the signals to permit reliable transmissions of the signals from the thin film head through the flexible circuit to the memory system controller. The thin film heads, rotating disc, arms, flexible circuits, servo mechanism and other related components are all contained within a sealed chassis referred to as the Head Disc Assembly (HDA). This seal chassis is necessary because the thin film head "flys" within a few microns of the rotating disc surface. Consequently, any contaminants within the system would act to foul the head/disc interface and disrupt the operation of the disc drive.
Currently, thin film heads of the type hereinabove discussed have three electrical connections to provide for the reading and writing functions. Future thin film heads for use with vertical recording methods may require more connections and possibly up to ten. Under present connection practice, the electrical connections between the thin film head and the arm flex circuit are made with very fine, i.e., #42 wire, which are soldered to pads at both ends. This is a manual operation resulting in high labor and assembly costs. Moreover, the very thin wires are small, fragile and easily damaged during assembly. As mentioned, reliability and contamination of the HDA are serious problems. The small connective wires are generally twisted into a small bundle. This wire bundle has undesirable electronic properties for signal transmission. Also, repair of the arm assembly is difficult because of the unsoldering and soldering which must occur (and which may contaminate the HDA). Typically, the entire arm assembly must be thrown away because of the difficulty of repair or damage occurring during the repair. As a consequence, replacement and repair costs of the date/servo flex circuit and magnetic head are quite high.